Long baseline RTK using a secondary base receiver and a non-continuous data link

ABSTRACT

The system and method for long baseline RTK survey are disclosed. The system includes a primary base station (PBS), a secondary base station (SBS), a primary data link between the PBS and the SBS, and a secondary data link between the SBS and a rover. The PBS, the SBS, and the rover are equipped with satellite antennas for satellite navigational purposes. The long baseline vector between the PBS and the rover is established by combining the primary baseline vector between the SBS and the PBS and the secondary baseline vector between the SBS and the rover. The PBS is placed in a position with a known location. The final SBS position is accurately determined using the PBS position during two initialization steps.

BACKGROUND

The Global Positioning System (GPS) is a system of satellite signaltransmitters that transmits information from which an observer's presentlocation and/or the time of observation can be determined. Anothersatellite-based navigation system is called the Global OrbitingNavigational System (GLONASS), which can operate as an alternative orsupplemental system.

The GPS was developed by the United States Department of Defense (DOD)under its NAVSTAR satellite program. A fully operational GPS includesmore than 21 Earth orbiting satellites approximately uniformly dispersedaround six circular orbits with four satellites each, the orbits beinginclined at an angle of 55° relative to the equator and being separatedfrom each other by multiples of 60° longitude. The orbits have radii of26,560 kilometers and are approximately circular. The orbits arenon-geosynchronous, with 0.5 sidereal day (11.967 hours) orbital timeintervals, so that the satellites move with time relative to the Earthbelow. Generally, four or more GPS satellites will be visible from mostpoints on the Earth's surface, and can be used to determine anobserver's position anywhere on the Earth's surface, 24 hours per day.Each satellite carries a cesium or rubidium atomic clock to providetiming information for the signals transmitted by the satellites. Aninternal clock correction is provided for each satellite clock.

Each GPS satellite continuously transmits two spread spectrum, L-bandcarrier signals: an L1 signal having a frequency f1=1575.42 MHz(nineteen centimeter carrier wavelength) and an L2 signal having afrequency f2=1227.6 MHz (twenty-four centimeter carrier wavelength).These two frequencies are integral multiplies f1=1,540 f0 and f2=1,200f0 of a base frequency f0=1.023 MHz. The deployment of additionalfrequencies is being planned by the DOD.

The L1 signal from each satellite is binary phase shift key (BPSK)modulated by two pseudo-random noise (PRN) codes in phase quadrature,designated as the C/A-code and P-code. The L2 signal from each satelliteis BPSK modulated by only the P-code. The nature of these PRN codes isdescribed below.

Use of PRN codes allows use of a plurality of GPS satellite signals fordetermining an observer's position and for providing the navigationinformation. A signal transmitted by a particular GPS satellite isselected by generating and matching, or correlating, the PRN code forthat particular satellite. Some of the PRN codes are known and aregenerated or stored in GPS satellite signal receivers operated by users.

A first known PRN code for each GPS satellite, sometimes referred to asa precision code or P-code, is a relatively long, fine-grained codehaving an associated clock or chip rate of f0=10.23 MHz. A second knownPRN code for each GPS satellite, sometimes referred to as aclear/acquisition code or C/A-code, is intended to facilitate rapidsatellite signal acquisition and hand-over to the P-code and is arelatively short, coarser-grained code having a clock or chip rate off0=1.023 MHz. The C/A -code for any GPS satellite has a length of 1023chips or time increments before this code repeats. The full P-code has alength of 259 days, with each satellite transmitting a unique portion ofthe full P-code. The portion of P-code used for a given GPS satellitehas a length of precisely one week (7.000 days) before this code portionrepeats.

Accepted methods for generating the C/A-code and P-code are set forth inthe document ICD-GPS-200: GPS Interface Control Document, ARINCResearch, 1997, GPS Joint Program Office, which is incorporated byreference herein.

The GPS satellite bit stream includes navigational information on theephemeris of the transmitting GPS satellite (which includes orbitalinformation about the transmitting satellite within next several hoursof transmission) and an almanac for all GPS satellites (which includes aless detailed orbital information about all other satellites). Thetransmitted satellite information also includes parameters providingcorrections for ionospheric signal propagation delays (suitable forsingle frequency receivers) and for an offset time between satelliteclock time and true GPS time. The navigational information istransmitted at a rate of 50 Baud.

A second satellite-based navigation system is the Global OrbitingNavigation Satellite System (GLONASS), placed in orbit by the formerSoviet Union and now maintained by the Russian Republic. GLONASS uses 24satellites, distributed approximately uniformly in three orbital planesof eight satellites each. Each orbital plane has a nominal inclinationof 64.8° relative to the equator, and the three orbital planes areseparated from each other by multiples of 120° longitude. The GLONASSsatellites have circular orbits with a radii of about 25,510 kilometersand a satellite period of revolution of 8/17 of a sidereal day (11.26hours). A GLONASS satellite and a GPS satellite will thus complete 17and 16 revolutions, respectively, around the Earth every 8 days. TheGLONASS system uses two carrier signals L1 and L2 with frequencies off1=(1.602+9k/16) GHz and f2=(1.246+7k/16) GHz, where k (=1,2, . . . 24)is the channel or satellite number. These frequencies lie in two bandsat 1.597-1.617 GHz (L1) and 1,240-1,260 GHz (L2). The L1 code ismodulated by a C/A-code (chip rate=0.511 MHz) and by a P-code (chiprate=5.11 MHz). The L2 code is presently modulated only by the P-code.The GLONASS satellites also transmit navigational data at a rate of 50Baud. Because the channel frequencies are distinguishable from eachother, the P-code is the same, and the C/A-code is the same, for eachsatellite. The methods for receiving and demodulating the GLONASSsignals are similar to the methods used for the GPS signals.

Reference to a Satellite Positioning System or SATPS herein refers to aGlobal Positioning System, to a Global Orbiting Navigation System, andto any other compatible satellite-based system that provides informationby which an observer's position and the time of observation can bedetermined, all of which meet the requirements of the present invention.

A Satellite Positioning System (SATPS), such as the Global PositioningSystem (GPS) or the Global Orbiting Navigation Satellite System(GLONASS), uses transmission of coded radio signals, with the structuredescribed above, from a plurality of Earth-orbiting satellites. A SATPSantenna receives SATPS signals from a plurality (preferably four ormore) of SATPS satellites and passes these signals to an SATPS signalreceiver/processor, which (1) identifies the SATPS satellite source foreach SATPS signal, (2) determines the time at which each identifiedSATPS signal arrives at the antenna, and (3) determines the presentlocation of the SATPS satellites.

The range (r_(i)) between the location of the i-th SATPS satellite andthe SATPS receiver is equal to the speed of light c times (Δt_(i)),wherein (Δt_(i) ) is the time difference between the SATPS receiver'sclock and the time indicated by the satellite when it transmitted therelevant phase. However, the SATPS receiver has an inexpensive quartzclock which is not synchronized with respect to the much more stable andprecise atomic clocks carried on board the satellites. Consequently, theSATPS receiver estimates a pseudo-range (pr_(i)) (not a true range) toeach satellite.

After the SATPS receiver determines the coordinates of the i-th SATPSsatellite by demodulating the transmitted ephemeris parameters, theSATPS receiver can obtain the solution of the set of the simultaneousequations for its unknown coordinates (x₀, y_(0,)z₀) and for unknowntime bias error (cb). The SATPS receiver can also determine velocity ofa moving platform.

The following discussion is applicable to any satellite navigationalsystem, but is focused on GPS applications to be substantially specific.

Differential Global Positioning System (DGPS) is a technique thatsignificantly improves both the accuracy and the integrity of the GlobalPositioning System (GPS). The most common version of DGPS requireshigh-quality GPS “reference receivers” at known, surveyed locations. Thereference station estimates the slowly varying error components of eachsatellite range measurement and forms a correction for each GPSsatellite in view. This correction is broadcast to all DGPS users on aconvenient communication link. Typical ranges for a local areadifferential GPS (LADGPS) station are up to 150 km. Within thisoperating range, the differential correction greatly improves accuracyfor all users, regardless of whether selective availability (SA) isactivated or is not. This improvement in the accuracy of the GlobalPositioning System (GPS) is possible because the largest GPS errors varyslowly with time and are strongly correlated over distance. DGPS alsosignificantly improves the “integrity” of GPS for all classes of users,because it reduces the probability that a GPS user would suffer from anunacceptable position error attributable to an undetected system fault.Expected accuracies with DGPS are within the range from 1 to 5 meters.

Most DGPS systems use a single reference station to develop a scalarcorrection to the code-phase measurement. If the correction is deliveredwithin 10 seconds, and the user is within 1000 km, the user accuracyshould be between 1 and 10 meters.

Network of reference stations can be used to form a vector correctionfor each satellite. This vector consists of individual corrections forthe satellite clock, three components of satellite positioning error (orephemeris), and parameters of an ionospheric delay model. The validityof this correction still decreases with increased latency or age of thecorrection. However, compared to a scalar correction, a vectorcorrection is valid over much greater geographical areas. This conceptis called wide area DGPS, or WADGPS. Such network can be used forcontinental or even world-hemisphere coverage, because it requires manyfewer reference stations than a collection of independent systems withone reference station each, and because it requires less communicationcapacity than the equivalent network of LADGPS systems.

Users with very stringent accuracy requirements may be able to use atechnique called carrier-phase DGPS or CDPGS. These users measure thephase of the GPS carrier relative to the carrier phase at a referencesite; thus achieving range measurement precision that is a few percentof the carrier wavelength, typically about one centimeter. These GPSphase comparisons are used for vehicle: attitude determination and alsoin survey applications, where the antennas are separated by tens ofkilometers. If the antennas are fixed, then the survey is called,static, and millimeter accuracies are possible, because long averagingtimes can be used to combat random noise. If the antennas are moving,then the survey is kinematic, and shorter time constants should be usedwith some degradation of accuracy. Summary of differential GPS conceptsand accuracies are given in Table I.

TABLE I Carrier phase measurements Code phase measurements World- SPSwide w/SA; SPS w/o SA, PPS. Up to Wide 3000 Area Km DGPS Up to Local 200Km area code DGPS Up to 50 Static Kinematic Dynamics Km Survey SurveyCDGPS Base/ 1 mm 1 cm 10 cm 1 m 10 m 100 m accuracy

The given above discussion can be found in “Global Positioning System:Theory and Applications”, Volume II, Chapter 1, by Bradford W. Parkinsonand James J. Spilker Jr., published by the American Institute ofAeronautics and Astronautics, Inc. in 1996.

For CDGPS, the definition of long baseline is arbitrary, but usuallyrefers to baseline lengths exceeding 20 km and up to 100 km. Lines inexcess of 100 km may be referred to as very long baselines.

There are two major difficulties with Long Baseline RTK (LBRTK).

(1) Processing in real-time the combined base and rover GPS measurementsto yield the baseline vectors with sufficient accuracy—which impliesfixed integer multi-frequency solutions; and

(2) broadcasting the base (or reference) station GPS data to the rovingstation (rover), for example using a protocol such as the TrimbleCompact Measurement record (Trimble CMR) data format, that was describedin the paper “Compact Data Transmission Standard for High-Precision GPS”given by Dr. Nicholas C. Talbot at The Proceedings of the IX-thInternational Technical Meeting of the Satellite Division of theInstitute of Navigation in the Kansas City, Mo., Sep. 13-20, 1996.

The first problem arises because atmospheric refraction of the satellitesignals which has different magnitudes at the two stations makesprocessing the data over a long baseline with high accuracy verydifficult. There are various ways to reduce these effects and increasebaseline accuracy. For instance, the errors caused by ionosphericrefraction can be reduced by combining satellite signals at two or moredistinct frequencies and forming ionospheric-free measurements, whilethe errors caused by tropospheric refraction can be reduced by using atropospheric model which can take into account the differences in theheight between the two stations. Thus, despite the inherent errors causeby signals refraction, it is possible to compute accurate longbaselines.

However, the second problem persists. Indeed, the problem ofbroadcasting the base station GPS data is difficult to solve due toradio licensing restrictions. The available bands in the frequencyspectrum, the transmit bandwidth at specific frequencies, and thetransmit power are regulated by agencies (for instance, FCC in the USA).Although, it is possible to obtain a license, it may not be possible toguarantee the availability of a clear channel for continuous datatransmission. A conventional RTK system requires a clear channel for itoperation. If the base station data cannot be received, the rover cannotcompute relative positions in real time. Problems also occur due to thedistance and the available transmit power. The signal may not havesufficient power to be received, or may be attenuated if there is noclear line of sight between the base and rover. Topology or foliage mayblock the signal entirely, depending on the transmit frequency.

Methods other than direct wireless links, for example, the cellulartelephone, can be used between the base and rover. However, a continuouslink may not be guaranteed if the rover moves between cells in thenetwork. If cellular links are being used, they also suffer from datalatency (a delay in the data that in turn delays computation of theposition of the rover), and from high telephone connection charges.

What is needed is a system and method for LBRTK that (1) utilizes anon-continuous link between the base and rover, and (2) minimizes highconnection charges by minimizing the amount of data needed to betransmitted from the base to the rover.

SUMMARY

The present invention is unique and novel because it discloses a systemand method for LBRTK surveying using a non-continuous data link betweena primary base station and a secondary base station (the significantportion of the baseline length), together with a secondary base stationand a much shorter continuous one-way secondary data link to the rover.Although the system requires a total of three satellite receivers, itdoes not suffer from the complications inherent in network RTK systemwhich typically require four or more receivers (three or more of whichcomprise the network which should be placed at known locations). Thesecondary base can be placed at an arbitrary location, for example at anelevated site providing clear reception of the secondary base from therover. This elevated site may also provide clear communication betweenthe primary and secondary bases if this data link is optionally a directradio link. The primary base can be used to service a number ofsecondary bases at different survey sites.

One aspect of the present invention is directed to a system for longbaseline real time kinematic positioning (LBRTK).

In one embodiment, the system comprises: (1) a primary base station(PBS); (2) a secondary base station (SBS); (3) a primary data linkbetween the SBS and the PBS; and (4) a secondary data link between theSBS and a rover.

In one embodiment, the PBS is configured to transmit data to the SBSusing the primary data link, the SBS is configured to compute asecondary base position SBS_P) relative to a primary base position(PBS_P) using the transmitted data from the PBS; and the rover isconfigured to perform an RTK survey using the SBS_P transmitted to therover using the secondary data link.

In one embodiment, the primary data link further comprises a primarytwo-way data link. The primary two-way data link can include: (1) acellular telephone link; (2) a radio link; (3) an electronic mail link;or (4) a satellite link.

In another embodiment, the primary data link further comprises a primaryone-way data link. In this embodiment, the PBS is configured to transmita compressed data set to the SBS according to a predetermined scheduleusing the primary one-way data link.

In one embodiment, the secondary data link further comprises a secondaryone-way data link. The secondary one-way data link can include: (1) aradio link; or (2) an optical link.

Another aspect of the present invention is directed to a system for longbaseline real time kinematic positioning (LBRTK) for a plurality ofrovers.

In one embodiment, the system comprises: (1) a primary base station(PBS); (2) a plurality of secondary base stations (SBS); (3) a pluralityof primary data links between the SBS and each PBS; and (4) a pluralityof secondary data links. Each SBS and each rover are linked by at leastone secondary data link.

One more aspect of the present invention is directed to a method forlong baseline real time kinematic positioning (LBRTK).

In one embodiment, the method comprises the following steps: (a)receiving a first plurality of broadcast satellite signals by utilizinga primary base station (PBS) comprising a primary base multi-frequencysatellite antenna; (b) continuously obtaining a first plurality ofsatellite observables using a primary base satellite receiver configuredto utilize the first plurality of received satellite signals; (c)logging each satellite observable obtained from the first plurality ofreceived satellite signals at a first predetermined interval using aprimary base data storage; (d) receiving a second plurality of broadcastsatellite signals by using a secondary base station (SBS) comprising asecondary base multi-frequency Satellite antenna; (e) continuouslyobtaining a second plurality of satellite observables using the secondplurality of received satellite signals by utilizing a secondary basesatellite receiver; (f) logging each satellite observable obtained fromthe second plurality of received satellite signals at a secondpredetermined interval by utilizing a secondary base data storage; (g)transmitting the PBS logged data from the PBS to the SBS using a primarydata link; (h) computing a secondary base position (SBS_P) relative to aprimary base position (PBS_P) using the transmitted PBS data; and (i)performing an RTK survey by a rover, wherein the rover is configured toreceive the SBS_P transmitted to the rover using a secondary data linkbetween the SBS and the rover.

Yet, one more aspect of the present invention is directed to a method ofLong Base RTK (LBRTK) surveying of a plurality of survey marks employinga rover, a primary base station (PBS), and a secondary base station(SBS), wherein the SBS and the PBS comprise a long baseline.

In one embodiment, the method comprising the following steps: (a)setting up the PBS in a location having an known position; (b) settingup the SBS in a location having an unknown position, wherein the SBSlocation is set to provide a secondary conmmunication link to the rover;(c) starting the PBS to automatically log a first plurality of satelliteobservables at a first predetermined rate; (d) storing the continuouslylogged PBS data in a primary database storage; (e) starting the SBS toautomatically log a second plurality of satellite observables at asecond predetermined rate; (f) storing the continuously logged SBS datain a secondary database storage; (g) initiating by the SBS a primarytwo-way communication link between the PBS and the SBS; (h) sending arequest for a first PBS data transfer by the SBS to the PBS, wherein therequested first PBS data comprises PBS data logged during a time periodbetween a time instance when the SBS was turned on and a time instancewhen the first sending request was sent; (i) accessing the primary PBSdatabase storage, compressing the requested first PBS data, and sendingthe first requested compressed PBS data set to the SBS using the primarytwo-way communication link; (k) matching the first logged SBS data withthe first transmitted compressed PBS data set; (1) computing an initialsecondary base position (SBS_IP) relative to a primary base stationposition (PBS_P) by utilizing the first transmitted compressed PBS dataset and the first logged matched SBS data; (m) continuously transmittingfrom the SBS to the rover initial data using the secondary communicationlink, wherein the initial data includes the SBS_IP; and (n) performingRTK surveying of each survey mark by the rover.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a system for long baseline real time kinematicpositioning (LBRTK) comprising a primary base station (PBS), a secondarybase station (SBS), a primary data link between the SBS and the PBS, anda secondary data link between the SBS and a rover.

FIG. 2 shows a flow chart of basic steps of a method for long baselinereal time kinematic positioning (LBRTK) employing a PBS, an SBS, and arover.

FIG. 3 illustrates a method of RTK surveying of a plurality of surveymarks including a first initialization step.

FIG. 4 illustrates a flow chart of a number of steps including a secondinitialization step that is needed to enable the computation of a finalSBS position with an accuracy corresponding to the required surveyaccuracy.

FIG. 5 depicts a system for long baseline real time kinematicpositioning (LBRTK) for a plurality of secondary base stations (SBS).

FULL DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts a system (10) for long baseline real time kinematicpositioning (LBRTK).

In one embodiment, the system (10) comprises: a primary base station is(PBS) (12), a secondary base station (SBS) (26), a primary data link(18) between the SBS and the PBS, and a secondary data link (34) betweenthe SBS and a rover (32). The primary satellite antenna (16), thesecondary satellite antenna (22), and the rover satellite antenna (36)are configured to receive all of broadcast satellite signals from theSATPS satellite system including at least four visiblesatellite-vehicles (38, 40, 42, and 44).

In one embodiment, the SATPS comprises the GPS system, and four visiblesatellite-vehicles (38, 40, 42, and 44) are GPS satellites. In thisembodiment, the primary satellite antenna (16), the secondary satelliteantenna (22), and the rover satellite antenna (36) are configured toreceive all of broadcast GPS satellite signals (such as the L1 signal,the L2 signal, and additional signals, like L3, that may be providedeither encrypted or unencrypted to users).

In another embodiment, the SATPS comprises the GLONASS system, and fourvisible satellite-vehicles (38, 40, 42, and 44) are GLONASS satellites.Yet, in one more embodiment, the SATPS comprises the combinedGPS/GLONASS system, and four visible satellite-vehicles (38, 40, 42, and44) are GPS and/or GLONASS satellites.

In one embodiment, the primary base primary data link antenna (PB_PDL_A)(19) is configured to transmit data over the two-way primary data link(18) to the secondary base (SBS) (26) and is configured to receive datafrom the secondary base (SBS) (26) over the two-way primary data link(18).

In this embodiment, the secondary base primary data link antenna(SB_PDL_A) (21) is configured to transmit data over the two-way primarydata link (18) to the primary base (PBS) (12) and is configured toreceive data from the primary base (PBS) (12) over the two-way primarydata link (18).

The primary two-way data link can comprise: a cellular telephone link; aradio link; an electronic mail link; or a satellite link.

If the primary two-way data link comprises a radio link, the radio linkcan comprise a shared wireless link on a frequency that specifiespriority to other voice users over data traffic, thus permitting onlynon-continuous operation, for example, using the 450 MHz commercialband.

If the primary two-way data link comprises a cellular telephone link,the main concern is the obstructions and topology between the PBS, SBS,and cell site, which can affect the data transmission between the PBSand the SBS.

The satellite link between PBS and the SBS would not suffer from theabove mentioned restrictions.

In another embodiment, the PBS (12) is configured to transmit acompressed data set to the SBS (26) using the primary one-way data link(18) according to a predetermined schedule using the primary baseprimary data link antenna (PB_PDL_A) (19). In this embodiment, thesecondary base primary data link antenna (SB_PDL_A) (21) is configuredto receive data over the one-way primary data link (18) from the primarybase (PBS) (12).

The primary one-way data link can comprise a radio link. For example,every 15 minutes mark after each hour the PBS would transmit in the30-50 MHz, or 450 MHz band the data collected during the previous 15minute collection period. Techniques such as carrier detect can be usedbefore each record of data is broadcast to prevent interference withvoice channels on the same frequency (in accordance with licensingregulations). This satisfies the requirement that the primary data linkis not continuous, and has no effect on the RTK survey as this data istransferred only during the initialization steps (see discussion below).Using the 450 MHz UHF band imposes a restriction on the length of theprimary baseline due to transmit power. Other radio links, such as the30-50 MHz VHF band, may be better suited for the proposed system.

In one embodiment, the SBS (26) is configured to compute a secondarybase position (SBS_P) relative to a primary base position (PBS_P) usingthe transmitted data from the PBS. The secondary base secondary datalink antenna (SB_SDL_A) (24) is configured to transmit data includingthe secondary base position (SBS_P) relative to the primary baseposition (PBS_P) from the secondary base (SBS) to the rover (32) usingthe secondary data link (34).

In one embodiment, the rover data link antenna (R_DL_A) (35) isconfigured to receive the data from the SBS (26) using the secondarydata link (34). The secondary data link (34) can include a radio link,or an optical link.

In one embodiment, the rover (32) is configured to perform an RTK surveyusing the data including the SBS_P data transmitted to the rover usingthe secondary data link (34).

FIG. 2 illustrates the basic steps of the method (50) for LBRTK. The PBSincludes a primary base satellite receiver (not shown) that uses thereceived satellite signals (step 52) to continuously obtain satelliteobservables (step 54).

The PBS includes a primary base data storage (14) configured tocontinuously log at some rate all satellite observables from eachvisible satellites (step 56). These satellite observables for eachvisible (from the PBS point of view) satellite include: (1) carrierphase, (2) PRN code phase, (3) time tags, and (4) other data (such as“cycle-slip indicators”) required for the computation of baselinevectors between two base stations, PBS (12) and SBS (26).

In one embodiment, if, for example, these satellite observables arestored every second, a circular system of storage can be used, so thatonly data observed during the last time period (for instance, the lastone hour) is stored.

In another embodiment, all data can be stored and archived for apost-processing mode of operation.

In one embodiment, the SBS (26) includes a secondary base satellitereceiver (not shown) configured to continuously obtain satelliteobservables using the received satellite signals (step 58 of FIG. 2).

The SBS (26) also includes a secondary base data storage (30) configuredto log each satellite observable obtained from the second plurality ofreceived satellite signals at a second predetermined interval (step 62of FIG. 2). These satellite observables for each visible (from the SBSpoint of view) satellite comprise: (1) carrier phase, (2) PRN codephase, (3) time tags, and (4) other data used for computation a primarybaseline vector between the PBS and the SBS.

In one embodiment, the secondary data storage can store and archive allthe accumulated data for a further post-processing operation.

The PBS is located over a known survey mark. The SBS is located at anarbitrary location chosen to provide clear communication to the roverand a connection to the cellular telephone network. The SBS location canbe changed during the survey to ensure a reliable link to the rover.This will require the system to be initialized again (step 64). Theinitialization process is described below.

The surveyor desires to measure accurate baselines between the knownmark (PBS location) and the position of the rover (32). To achieve thisgoal, the surveyor can at first compute the baseline vector between thePBS and SBS (step 66 of FIG. 2), and secondly, compute the vectorbetween the SBS and the rover (32) (step 68 of FIG. 2).

The rover is configured to obtain its own satellite data by using itsown satellite antenna (36). The rover supplements its own satellite datawith the SBS_P data transmitted by using the secondary data link (34 ofFIG. 1) between the SBS and the rover. Thus, in this mode of practicingthe present invention, the rover is configured to perform RTK survey ofan area according to a predetermined plan utilizing the data transmittedto the rover along the long baseline.

From the surveyor's point of view, setting up the PBS and the SBS attheir respective locations, and switching on the units is all that isrequired. All operations at these sites are performed automatically bythe equipment. The surveyor starts the rover unit which may beoptionally connected to a handheld controller, and enables an RTKsurvey. Two initialization steps should occur before the rover is ableto compute accurate positions relative to the PBS and SBS positions, andrelative to the primary baseline vector between the PBS and SBS.

FIG. 3 illustrates a method (80) of RTK surveying of a plurality ofsurvey marks including a first initialization step.

The PBS is set up (step 82 of FIG. 3) in a location having an knownposition, wherein the SBS is set up (step 84 of FIG. 3) in an arbitrarylocation chosen to provide clear secondary communication link (34 ofFIG. 1) to the rover (32 of FIG. 1). In another embodiment, the SBS canbe placed over an existing survey mark, or over a newly created mark.The advantage of locating the SBS at any survey mark is that once theportion of the mark has been established by the second initializationstep (see discussion below), the SBS can be re-located elsewhere andthen moved back to the original mark without requiring any furtherinitialization, that is no further communication with the PBS isnecessary. Thus, the RTK survey in some future time can occur by simplyplacing the SBS over the established survey mark, and providing the SBSwith an identification code for the mark (for example, via a handheldcontroller). The SBS then retrieves its previously computed position(SBS_P) from its internal database, and includes this information in thedata message broadcast to the rover (see discussion below).

When the PBS is started (step 86 of FIG. 3), it automatically begins tolog satellite observables in a primary database storage (step 88) at apredetermined rate, for example, every 5 seconds. At this stage, thereis no communication between the PBS and SBS. At step (90), the SBSstarts to automatically log satellite observables at some rate, andstarts to store (step 92) the continuously logged SBS data in asecondary database storage.

After a short period of time, for example, 5 minutes, the SBS has loggedenough SBS data to compute SBS approximate position (SBS_P) relative tothe PBS.

If the primary data link (18) is a two-way link, the connection can beinitiated by the SBS (step 94), for instance, by calling up the PBS onthe telephone. If the line is busy, the SBS keeps retrying until itconnects. Following connection, the SBS requests (step 96) a datatransfer corresponding to the time period just elapsed, that is duringthe time period between a time instance when the SBS was turned on and atime instance when the first sending request was sent.

To prepare the requested data, the PBS accesses its database storage (14of FIG. 1), compresses the first requested set of PBS data to reduce thetransmission time, and sends the compressed PBS data set to the SBS(step 98). The amount of data, and thus the connection time, can bereduced if the SBS uses a longer logging interval itself. The data atthe PBS is then decimated (for example, only data on each 10 second markis provided) to match the SBS logging interval itself (step 100). Thecomputed SBS position (step 102) is referred to as the initial secondarybase position SBS_IP. The solution type may be float, i. e. the integerambiguities are not resolved.

If the SATPS system is GPS, any differential GPS solution may be used,including single-difference, double-difference, and triple-differencetechniques.

In another embodiment, a system of e-mail messages over the internet canbe used to implement the primary two-way data link (18 of FIG. 1). Ifthis is the case, an e-mail message is sent that indicates the timeperiod during which the requested data was logged. The data is returnedvia another e-mail. In this embodiment, it is necessary for the SBS tocontinuously or periodically check for the returned e-mail. Thiseliminates problem of a busy direct line to the PBS. Once the SBS hasestablished a connection to the internet server, the SBS simply sends ane-mail, and waits for a reply. The cost of an internet data link may beconsiderably less than the cost of a standard cellular telephone link.

As soon as the initial SBS position (SBS_P) is available, the firstinitialization step is complete. The rover can begin an RTK survey. TheSBS transmits continuous data to the rover (step 104) using thesecondary data link (34). In one embodiment, the secondary data link(34) comprises a local one-way radio link. In addition to the usual dataassociated with RTK surveying (for example the data in the Trimble CMRformat), the known position of the PBS (PBS_P) and the initial SBSposition (SBS_IP) is broadcast. Using these positions, and simple vectorarithmetic, the rover is able to compute its position relative to thePBS, i. e. relative to a long baseline. However, at this stage thisvector is of a limited accuracy depending on the accuracy of the initialSBS position (SBS_IP). All rover positions thus computed are flagged asinitial, indicating low accuracy. If the surveyor is identifyingexisting survey marks (step 106 of FIG. 3), this is not important, asthe positions can be adjusted at a later stage. However, if new surveymarks are being established from database of positions (a process knownas a stake-out), it is necessary to wait for the second and final stageof system initialization before starting to stake-out the new marks(unless lower accuracy is acceptable).

The accuracy of the initial SBS position (SBS_IP) should be sufficientto ensure that the accuracy of the computed rover position (relative tothe SBS) is not compromised. As the secondary baseline (rover/SBS) istypically short as compared to the primary baseline (PBS/SBS), theaccuracy of hiss secondary baseline is a weak function of the absolute(non-relative) accuracy of the computed SBS position (SBS_P), and isalso dependent on the secondary baseline length. Sufficient accuracy canbe obtained by increasing the logging period up to 5 minutes prior tocomputing the initial SBS position (SBS_IP) in the above-given example.

FIG. 4 illustrates a flow chart (120) of a number of steps including asecond initialization step that are needed to enable the computation ofa final SBS position with an accuracy corresponding to the requiredsurvey accuracy.

Throughout the first initialization step (including the transfer of datafrom the PBS), the SBS continues to log data at the original rate (stepnot shown). The second initialization step requires another datatransfer from the PBS. The total duration during which the requestedsecond data set was logged (the first portion of which comprises thelogged data used in the first initialization step) should besufficiently long to enable the computation of a final SBS position(SBS_FP) with an accuracy corresponding to the required rover surveyaccuracy. The duration is dependent on the primary baseline length (forexample, 20 minutes). While waiting for this time to elapse, RTKsurveying may continue at the rover (step 122). If required, thestake-out process can be performed with reduced accuracy, that is beforethe second initialization step is completed.

When the PBS data collection is complete (step 124), the SBS calls upthe PBS on the telephone as before (step 126), and transfers compressedand decimated data from the PBS (step 128). Using the larger data set,techniques similar to conventional static post-processing can be used toyield the final SBS position (SBS_FP) (step 130). This completes thesecond initialization step.

After the final SBS position (SBS_FP) is computed, the statisticalindicators should be checked (step 132) to insure that the finalposition is of a sufficient accuracy. If it is not the case, theadditional data may be required. The second initialization step can bepostponed while both the PBS and SBS collect additional data, and afurther connection and data transfer occurs between PBS and SBS. Toreduce the overall initialization time, it is desirable to attempt toinitialize as early as sufficient amount of additional data becomesavailable.

The final SBS position (SBS_FP) is transmitted from the SBS to the roverover the secondary data link (step 134). The SBS can use the differencebetween the initial (SBS_IP) and final (SBS_FP) SBS positions to correctall previously computed (PBS/rover) baselines stored in its surveydatabase.

Finally, the rover computes its final rover position relative to theSBS_FP using the final data transmitted from the SBS (step 136). Thefinal rover position determines a survey mark. An accurate stake-out canbe carried out by using a database of stake-out vectors between the PBSand the stake-out marks (step 138).

Further integrity can be provided by additional steps of connecting withthe PBS and transferring an additional satellite data after the secondinitialization step is completed. The additional data can be combinedwith previously downloaded data to improve accuracy of the final basepositions, or simply to check the accuracy. For example, a check can bemade to ensure that the data used to compute the final position was notcollected during a period of high multiptah distortions.

In one embodiment, the rover is not required at all. In this embodiment,the SBS is used to establish the positions of existing or newly createdsurvey marks. Essentially, the second initialization step becomes themethod of position determination. The technique is similar totraditional static survey post-processing, except that all processingoccurs within the SBS (or within an associated handheld controller), andthe position is available in the field. Positions obtained in thisembodiment of the invention can be used later for RTK surveying withjust the SBS and a rover.

In another embodiment of the present invention, FIG. 5 depicts a system(150) for long baseline real time kinematic positioning (LBRTK)including a plurality of secondary base stations (SBS) (156, 166, 172).

The system (150) comprises: a primary base station (PBS) (152) includinga primary data storage (154), a primary radio antenna (160), and aprimary satellite antenna (not shown). The system (150) further includesa plurality of secondary base stations (SBS) (156, 166, 172). Eachsecondary base station (SBS) (156, 166, and 172) includes a secondarydata storage (158, 168, and 174 respectively), a secondary receiving andtransmitting radio antenna (162, 164, and 170 respectively), and asecondary satellite antenna (not shown). Each secondary base station(SBS) (156, 166, and 172) is linked to the PBS (152) by one primary datalink (176, 178, and 180 respectively). Each primary data link can be atwo-way data link, or a one-way data link (see discussion above). Eachsecondary base station (SBS) (156, 166, 172) is linked to at least onerover (190, 194, and 198 respectively) by using one secondary data link(182, 184, and 186 respectively). Each rover (190, 194, and 198)includes a radio antenna (188, 192, and 196 respectively) and asatellite antenna (not shown).

The primary data link is used only during the two initialization steps(see discussion above). At all other times the PBS is free tocommunicate with all other SBS receivers at other sites. Therefore, asingle PBS can be used to provide service over a large area to manysurvey crews provided that short delays can be tolerated when PBS isbusy communicating with another SBS. In one embodiment, a singletelephone number or a single e-mail address can be provided to all SBSfor access to the PBS.

The description of the preferred embodiment of this invention is givenfor the purposes of explaining the principles thereof, and is not to beconsidered as limiting or restricting the invention since manymodifications may be made by the exercise of skill in the art withoutdeparting from the scope of the invention.

What is claimed is:
 1. A system for long baseline real time kinematicpositioning (LBRTK) comprising: a primary base station (PBS); asecondary base station (SBS); a primary data link between said SBS andsaid PBS; and a secondary data link between said SBS and a rover;wherein said PBS is configured to transmit data to said SBS using saidprimary data link, and wherein said SBS is configured to compute asecondary base position (SBS_P) relative to a primary base position(PBS_P) using said transmitted data from said PBS; and wherein saidrover is configured to perform an RTK survey using said SBS_Ptransmitted to said rover using said secondary data link.
 2. The systemof claim 1, wherein said PBS further comprises: a primary basemulti-frequency satellite antenna configured to receive a firstplurality of broadcast satellite signals; a primary base satellitereceiver configured to continuously obtain a first plurality ofsatellite observables using said first plurality of received satellitesignals; and a primary base data storage configured to log each saidsatellite observable obtained from said first plurality of receivedsatellite signals at a first predetermined interval.
 3. The system ofclaim 1, wherein said PBS further comprises: a primary basemulti-frequency satellite antenna configured to receive a firstplurality of broadcast satellite signals; and a primary base satellitereceiver configured to continuously obtain a first plurality ofsatellite observables using said first plurality of received satellitesignals.
 4. The system of claim 2, wherein said SBS further comprises: asecondary base multi-frequency satellite antenna configured to receive asecond plurality of broadcast satellite signals; a secondary basesatellite receiver configured to continuously obtain a second pluralityof satellite observables using said second plurality of receivedsatellite signals; and a secondary base data storage configured to logeach said satellite observable obtained from said second plurality ofreceived satellite signals at a second predetermined interval.
 5. Thesystem of claim 1, wherein said SBS further comprises: a secondary basemulti-frequency satellite antenna configured to receive a secondplurality of broadcast satellite signals; and a secondary base satellitereceiver configured to continuously obtain a second plurality ofsatellite observables using said second plurality of received satellitesignals.
 6. The system of claim 1, wherein said primary data linkfurther comprises: a primary two-way data link.
 7. The system of claim6, wherein said primary two-way data link further comprises: a cellulartelephone link.
 8. The system of claim 6, wherein said primary two-waydata link further comprises: a radio link.
 9. The system of claim 6,wherein said primary two-way data link further comprises: an electronicmail link.
 10. The system of claim 6, wherein said primary two-way datalink further comprises: a satellite link.
 11. The system of claim 1,wherein said primary data link further comprises: a primary one-way datalink, wherein said PBS is configured to transmit a compressed data setto said SBS using said primary one-way data link according to apredetermined schedule.
 12. The system of claim 1, wherein saidsecondary data link further comprises: a secondary one-way data link.13. The system of claim 12, wherein said secondary one-way data linkfurther comprises: a radio link.
 14. The system of claim 12, whereinsaid secondary one-way data link further comprises: an optical link. 15.The system of claim 4; wherein said primary base data storage furthercomprises: a circular storage system configured to log a plurality ofcarrier phases, and time tags for said first plurality of satelliteobservables; wherein said secondary base data storage further comprises:a data storage system configured to log a plurality of carrier phases,and time tags for said second plurality of satellite observables; andwherein said PBS data logged in said circular storage system and saidSBS data logged in said data storage system are used for computation aprimary baseline vector between said PBS and said SBS.
 16. A system forlong baseline real time kinematic positioning (LBRTK) for a plurality ofrovers comprising: a primary base station (PBS); a plurality ofsecondary base stations (SBS); a plurality of primary data links betweensaid SBS and each said PBS; and a plurality of secondary data links,wherein each said SBS and each said rover are linked by at least onesaid secondary data link; wherein said PBS is configured to transmit acompressed data set to each said SBS using one said primary data link;and wherein each said SBS is configured to compute one said secondarybase position (SBS_P) relative to a primary base position (PBS_P) usingsaid transmitted compressed data set from said PBS; and wherein eachsaid rover is configured to perform an RTK survey using at least onesaid SBS_P transmitted to said rover using at least one said secondarydata link.
 17. A system for long baseline real time kinematicpositioning (LBRTK) comprising: a secondary base station (SBS); aprimary data link between said SBS and a primary base station (PBS); anda secondary data link between said SBS and a rover; wherein said PBS isconfigured to transmit a compressed data set to said SBS using saidprimary data link, and wherein said SBS is configured to compute asecondary base position (SBS_P) relative to a primary base position(PBS_P) using said transmitted compressed data set from said PBS; andwherein said rover is configured to perform an RTK survey using saidSBS_P transmitted to said rover using said secondary data link.
 18. Asystem for long baseline real time kinematic positioning (LBRTK) for aplurality of rovers comprising: a plurality of secondary base stations(SBS); a plurality of primary data links between each said SBS and aprimary base station (PBS); and a plurality of secondary data linksbetween a plurality of rovers and said plurality of SBS, wherein eachsaid SBS and each said rover are linked by using at least one saidsecondary data link; wherein said PBS is configured to transmit acompressed data set to each said SBS using one said primary data link;and wherein each said SBS is configured to compute one said secondarybase position (SBS_P) relative to a primary base position (PBS_P) usingsaid transmitted compressed data set from said PBS; and wherein eachsaid rover is configured to perform an RTK survey using at least onesaid SBS_P transmitted to said rover using at least one said secondarydata link.
 19. A method for long baseline real time kinematicpositioning (LBRTK) comprising the following steps: (a) receiving afirst plurality of broadcast satellite signals by utilizing a primarybase station (PBS) comprising a primary base multi-frequency satelliteantenna; (b) continuously obtaining a first plurality of satelliteobservables using a primary base satellite receiver configured toutilize said first plurality of received satellite signals; (c) loggingeach said satellite observable obtained from said first plurality ofreceived satellite signals at a first predetermined interval using aprimary base data storage; (d) receiving a second plurality of broadcastsatellite signals by using a secondary base station (SBS) comprising asecondary base multi-frequency Satellite antenna; (e) continuouslyobtaining a second plurality of satellite observables using said secondplurality of received satellite signals by utilizing a secondary basesatellite receiver; (f) logging each said satellite observable obtainedfrom said second plurality of received satellite signals at a secondpredetermined interval by utilizing a secondary base data storage; (g)transmitting said PBS logged data from said PBS to said SBS using aprimary data link; (h) computing a secondary base position (SBS_P)relative to a primary base position (PBS_P) using said transmitted PBSdata; wherein said SBS_P relative to said PBS_P comprises a primarybaseline; and (i) performing an RTK survey by a rover, wherein saidrover is configured to receive said SBS_P transmitted to said roverusing a secondary data link between said SBS and said rover.
 20. Themethod of claim 19, wherein said step (g) of transmitting said PBSlogged data from said PBS to said SBS using said primary data linkfurther includes the steps of: transmitting a request for said PBS datato said PBS using a two-way primary data link between said PBS and saidSBS; and transmitting said requested PBS data to said SBS from said PBSusing said two-way primary data link.
 21. The method of claim 19,wherein said step (g) of transmitting said PBS logged data from said PBSto said SBS using said primary data link further includes the steps of:transmitting said PBS logged data to said SBS from said PBS using saidone-way primary data link according to a predetermined schedule.
 22. Amethod of RTK surveying of a plurality of survey marks employing arover, a primary base station (PBS), and a secondary base station (SBS),wherein said SBS and said PBS comprise a long baseline, said methodcomprising the steps of: (a) setting up said PBS in a location having anknown position; (b) setting up said SBS in a location having an unknownposition, wherein said SBS location is set to provide a secondarycommunication link to said rover; (c) starting said PBS to automaticallylog a first plurality of satellite observables at a first predeterminedrate; (d) storing said continuously logged PBS data in a primarydatabase storage; (e) starting said SBS to automatically log a secondplurality of satellite observables at a second predetermined rate; (f)storing said continuously logged SBS data in a secondary databasestorage; (g) initiating by said SBS a primary two-way communication linkbetween said PBS and said SBS; (h) sending a request for a first PBSdata transfer by said SBS to said PBS, wherein said requested first PBSdata comprises PBS data logged during a time period between a timeinstance when said first sending request was sent and a time instancewhen said SBS was turned on; (i) accessing said primary PBS databasestorage, compressing said requested first PBS data, and sending saidfirst requested compressed PBS data set to said SBS using said primarytwo-way communication link; (k) matching said first logged SBS data withsaid first transmitted compressed PBS data set; (l) computing an initialsecondary base position (SBS_P) relative to a primary base stationposition (PBS_P) by utilizing said first transmitted compressed PBS dataset and said first logged matched SBS data; (m) continuouslytransmitting from said SBS to said rover initial data using saidsecondary communication link, wherein said initial data includes saidSBS_IP; and (n) performing RTK surveying of each said survey mark bysaid rover.
 23. The method of claim 22, wherein said step (n) ofperforming said RTK surveying of a plurality of survey marks by saidrover further includes the steps of: (n1) performing RTK surveying of afirst survey mark by computing an initial rover position relative tosaid SBS_P using said initial data transmitted from said SBS; whereinsaid rover position relative to said SBS_IP comprises a secondarybaseline; and by adjusting said initial rover position; and (n2)repeating said step (n1) for each said survey mark.
 24. The method ofclaim 22, wherein said step (n) of performing said RTK surveying by saidrover a plurality of survey marks further includes the steps of: (n1)computing an initial rover position relative to said SBS using saidinitial data transmitted from said SBS; (n2) continuously logging saidPBS data at said first predetermined rate and storing said continuouslylogged PBS data in said primary database storage; (n3) sending a secondrequest for a PBS data transfer by said SBS to said PBS, wherein saidrequested second PBS data comprises final PBS data logged during a finaltime period substantially sufficient to enable the computation of afinal SBS_P (SBS_FP) with a required accuracy; (n4) accessing saidprimary PBS database storage, compressing said second requested loggedPBS data, and sending said second compressed PBS data set to said SBSusing said primary two-way communication link; (n5) computing said finalsecondary base position (SBS_FP) relative to a primary base stationposition (PBS_P) by using a post-processing technique; (n6) checking aplurality of statistical indicators to ensure a correct solution forsaid SBS_FP; (n7) continuously transmitting from said SBS to said roverfinal data including said SBS_FP using said secondary communicationlink; (n8) computing a final rover position relative to said SBS usingsaid final data transmitted from said SBS; wherein said final roverposition determines a first survey mark; and (n9) repeating said steps(n1-n8) for each said survey mark.
 25. The method of claim 24, whereinsaid step (n3) of sending a second request for a PBS data transferfurther includes the step of: checking the level of multipath distortionduring said final time period of PBS data logging.
 26. A method of RTKsurveying of a plurality of survey marks employing a rover, a primarybase station (PBS), and a secondary base station (SBS), wherein said SBSand said PBS comprise a long baseline, said method comprising the stepsof: (a) setting up said PBS in a location having an known position; (b)setting up said SBS in a location having an unknown position, whereinsaid SBS location is set to provide a secondary communication link tosaid rover; (c) starting said PBS to automatically log a first pluralityof satellite observables at a first predetermined rate; (d) storing saidcontinuously logged PBS data in a primary database storage; (e) startingsaid SBS to automatically log a second plurality of satelliteobservables at a second predetermined rate; (f) storing saidcontinuously logged SBS data in a secondary database storage; (g)accessing said primary PBS database storage, compressing first PBS data,and sending said first compressed PBS data set to said SBS using aone-way primary communication link according to a predeterminedschedule; (h) matching said first logged SBS data with said firsttransmitted compressed PBS data set; (i) computing an initial secondarybase position (SBS_P) relative to a primary base station position(PBS_P) by utilizing said first transmitted compressed PBS data set andsaid first logged matched SBS data; (k) continuously transmitting fromsaid SBS to said rover initial data using said secondary communicationlink, wherein said initial data includes said SBS_IP; and (l) performingRTK surveying by said rover.
 27. The method of claim 26, wherein saidstep (l) of performing said RTK surveying of a plurality of survey marksby said rover further includes the step of: (l1) performing RTK surveyof a first survey mark by computing an initial rover position relativeto said SBS_P using said initial data transmitted from said SBS; whereinsaid rover position relative to said SBS_P comprises a secondarybaseline; and by adjusting said initial rover position; and (l2)repeating said step (l1) for each said survey mark.
 28. The method ofclaim 26, wherein said step (l) of performing said RTK surveying of aplurality of survey marks by said rover further includes the steps of:(l1) computing an initial rover position relative to said SBS using saidinitial data transmitted from said SBS; (l2) continuously logging saidPBS data at said first predetermined rate and storing said continuouslylogged PBS data in said primary database storage; (l3) accessing saidprimary PBS database storage, compressing second logged PBS data, andsending said second compressed PBS data to said SBS using said primaryone-way communication link; (l4) computing a final secondary baseposition (SBS_FP) relative to a primary base station position (PBS_P) byusing a post-processing technique; (l5) checking a plurality ofstatistical indicators to ensure a correct solution for said SBS_FP;(l6) continuously transmitting from said SBS to said rover final dataincluding said SBS_FP using said secondary communication link; (l7)performing RTK survey of a first survey mark by computing a final roverposition relative to said SBS using said final data transmitted fromsaid SBS; and (l8) repeating said steps (l1-l7) for each said surveymark.
 29. A method for long baseline real time kinematic positioning(LBRTK) comprising the following steps: (a) receiving a first pluralityof broadcast satellite signals by utilizing a primary base station (PBS)comprising a primary base multi-frequency satellite antenna; (b)continuously obtaining a first plurality of satellite observables usinga primary base satellite receiver configured to utilize said firstplurality of received satellite signals; (c) logging each said satelliteobservable obtained from said first plurality of received satellitesignals at a first predetermined interval using a primary base datastorage; (d) receiving a second plurality of broadcast satellite signalsby using a secondary base station (SBS) comprising a secondary basemulti-frequency Satellite antenna; (e) continuously obtaining a secondplurality of satellite observables using said second plurality ofreceived satellite signals by utilizing a secondary base satellitereceiver; (f) logging each said satellite observable obtained from saidsecond plurality of received satellite signals at a second predeterminedinterval by utilizing a secondary base data storage; (g) transmittingsaid PBS logged data from said PBS to said SBS using a primary datalink; (h) computing a secondary base position (SBS_P) relative to aprimary base position (PBS_P) using said transmitted PBS data; whereinsaid SBS_P relative to said PBS_P comprises a primary baseline; and (i)transmitting said SBS_P to a rover using a secondary data link betweensaid SBS and said rover.
 30. The method of claim 29, wherein said step(g) of transmitting said PBS logged data from said PBS to said SBS usingsaid primary data link further includes the steps of: transmitting arequest for said PBS data to said PBS using a two-way primary data linkbetween said PBS and said SBS; and transmitting said requested PBS datato said SBS from said PBS using said two-way primary data link.
 31. Themethod of claim 29, wherein said step (g) of transmitting said PBSlogged data from said PBS to said SBS using said primary data linkfurther includes the steps of: transmitting said PBS logged data to saidSBS from said PBS using said one-way primary data link according to apredetermined schedule.
 32. A method of RTK surveying comprising thesteps of: (1) setting up a primary base station (PBS) in a locationhaving an known position; (2) setting up a secondary base station (SBS)in a location having an unknown position, wherein said SBS location isset to provide a secondary communication link to a rover; (3) startingsaid PBS to automatically log a first plurality of satellite observablesat a first predetermined rate; (4) storing said continuously logged PBSdata in a primary database storage; (5) starting said SBS toautomatically log a second plurality of satellite observables at asecond predetermined rate; (6) storing said continuously logged SBS datain a secondary database storage; (7) initiating by said SBS a primarytwo-way communication link between said PBS and said SBS; (8) sending arequest for a first PBS data transfer by said SBS to said PBS, whereinsaid requested first PBS data comprises PBS data logged during a timeperiod between a time instance when said first sending request was sentand a time instance when said SBS was turned on; (9) accessing saidprimary PBS database storage, compressing said requested first PBS data,and sending said first requested compressed PBS data set to said SBSusing said primary two-way communication link; (10) matching said firstlogged SBS data with said first transmitted compressed PBS data set;(11) computing an initial secondary base position (SBS_IP) relative to aprimary base station position (PBS_P) by utilizing said firsttransmitted compressed PBS data set and said first logged matched SBSdata; (12) transmitting from said SBS to said rover initial data usingsaid secondary communication link, wherein said initial data includessaid SBS_P; (13) sending a second request for a PBS data transfer bysaid SBS to said PBS, wherein said requested second PBS data comprisesfinal PBS data logged during a final time period substantiallysufficient to enable the computation of a final SBS_P (SBS_FP) with arequired accuracy; (14) accessing said primary PBS database storage,compressing said second requested logged PBS data, and sending saidsecond compressed PBS data set to said SBS using said primary two-waycommunication link; (15) computing said final secondary base position(SBS_FP) relative to a primary base station position (PBS_P) by using apost-processing technique; (16) checking a plurality of statisticalindicators to ensure a correct solution for said SBS_FP; and (17)transmitting from said SBS to said rover a final data including saidSBS_FP using said secondary communication link.
 33. A method of RTKsurveying comprising the steps of: (1) setting up a primary base station(PBS) in a location having an known position; (2) setting up a secondarybase station (SBS) in a location having an unknown position, whereinsaid SBS location is set to provide a secondary communication link to arover; (3) starting said PBS to automatically log a first plurality ofsatellite observables at a first predetermined rate; (4) storing saidcontinuously logged PBS data in a primary database storage; (5) startingsaid SBS to automatically log a second plurality of satelliteobservables at a second predetermined rate; (6) storing saidcontinuously logged SBS data in a secondary database storage; (7)accessing said primary PBS database storage, compressing first PBS data,and sending said first compressed PBS data set to said SBS using aone-way primary communication link according to a predeterminedschedule; (8) matching said first logged SBS data with said firsttransmitted compressed PBS data set; (9) computing an initial secondarybase position (SBS_IP) relative to a primary base station position(PBS_P) by utilizing said first transmitted compressed PBS data and saidfirst logged matched SBS data; (10) transmitting from said SBS to saidrover an initial data using said secondary communication link, whereinsaid initial data includes said SBS_IP; (11) accessing said primary PBSdatabase storage, compressing second logged PBS data, and sending saidsecond compressed PBS data set to said SBS using said primary one-waycommunication link according to said predetermined schedule; (12)computing said final secondary base position (SBS_FP) relative to aprimary base station position (PBS_P) by using a post-processingtechnique; (13) checking a plurality of statistical indicators to ensurea correct solution for said SBS_FP; and (14) transmitting from said SBSto said rover final data including said SBS_FP using said secondarycommunication link.
 34. A method for long baseline real time kinematicpositioning (LBRTK) comprising the following steps: (a) receiving aplurality of broadcast satellite signals by using a secondary basestation (SBS) comprising a secondary base multi-frequency Satelliteantenna; (b) continuously obtaining a plurality of satellite observablesusing said plurality of received satellite signals by utilizing asecondary base satellite receiver; (c) logging each said satelliteobservable obtained from said plurality of received satellite signals ata predetermined interval by utilizing a secondary base data storage; (d)receiving primary base station (PBS) logged data using a primary datalink; (e) computing a secondary base position (SBS_P) relative to aprimary base position (PBS_P) using said transmitted PBS data; whereinsaid SBS_P relative to said PBS_P comprises a primary baseline; and (f)transmitting to a rover said SBS_P data using a secondary data linkbetween said SBS and said rover.
 35. A method of RTK surveyingcomprising the steps of: (1) setting up a secondary base station (SBS)in a location having an unknown position, wherein said SBS location isset to provide a secondary communication link to a rover; (2) startingsaid SBS to automatically log a plurality of satellite observables at apredetermined rate; (3) storing said continuously logged SBS data in asecondary database storage; (4) initiating by said SBS a primary two-waycommunication link between said SBS and a primary base station (PBS);(5) sending a request for a first PBS data transfer by said SBS to saidPBS, wherein said requested first PBS data comprises PBS data loggedduring a time period between a time instance when said first sendingrequest was sent and a time instance when said SBS was turned on; (6)receiving said first requested PBS data from said SBS using said primarytwo-way communication link; (7) matching said first logged SBS data withsaid first transmitted PBS data; (8) computing an initial secondary baseposition (SBS_P) relative to a primary base station position (SBS_P) byutilizing said first transmitted PBS data and said first logged matchedSBS data; (9) transmitting from said SBS to said rover an initial dataset using said secondary communication link, wherein said initial dataincludes said SBS_IP; (10) sending a second request for PBS datatransfer by said SBS to said PBS, wherein said requested second PBS datacomprises a final PBS data set logged during a final time periodsubstantially sufficient to enable the computation of a final SBS_P(SBS_FP) with a required accuracy; (11) receiving said second compressedPBS data set from said SBS using said primary two-way communicationlink; (12) computing said final secondary base position (SBS_FP)relative to a primary base station position (PBS_P) by using apost-processing technique; (13) checking a plurality of statisticalindicators to ensure a correct solution for said SBS_FP; and (14)transmitting from said SBS to said rover a final data set including saidSBS_FP using said secondary communication link.
 36. A method of RTKsurveying comprising the steps of: (1) setting up a secondary basestation (SBS) in a location having an unknown position, wherein said SBSlocation is set to provide a secondary communication link to a rover;(2) starting said SBS to automatically log a plurality of satelliteobservables at a predetermined rate; (3) storing said continuouslylogged SBS data in a secondary database storage; (4) receiving a firstPBS data set from said SBS using a primary one-way communication linkaccording to a predetermined schedule; (5) matching said first loggedSBS data with said first transmitted PBS data; (6) computing an initialsecondary base position (SBS_IP) relative to a primary base stationposition (PBS_P) by utilizing said first transmitted PBS data and saidfirst logged matched SBS data; (7) transmitting from said SBS to saidrover initial data using said secondary communication link, wherein saidinitial data includes said SBS_IP; (8) receiving a second PBS data setfrom said SBS using said primary one-way communication link according tosaid predetermined schedule, wherein said second PBS data comprisesfinal PBS data logged during a final time period substantiallysufficient to enable the computation of a final SBS_P (SBS_FP) with arequired accuracy; (9) computing said final secondary base position(SBS_FP) relative to a primary base station position (PBS_P) by using apost-processing technique; (10) checking a plurality of statisticalindicators to ensure a correct solution for said SBS_P; and (11)transmitting from said SBS to said rover final data including saidSBS_FP using said secondary communication link.